Methods and systems for biomass conversion to carboxylic acids and alcohols

ABSTRACT

The disclosure includes a method, process and apparatus for the conversion of biomass to carboxylic acids and/or primary alcohols. The system may include a pretreatment/fermentation subsystem operable to produce a fermentation broth containing carboxylic acid salts from biomass, such as lignocellulosic biomass. The system may also include a dewatering subsystem operable to remove excess water from the fermentation broth to produce a concentrated product. The system may also includes an acid springing subsystem operable to produce a mixed carboxylic acid product. The system may also include a hydrogenation subsystem operable to produce an alcohol mixture, such as a mixture containing primary alcohols. Methods of operating this system or other systems to obtain a carboxylic acid or alcohol mixture are also provided.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Application No.60/580,291 filed Jun. 16, 2004.

TECHNICAL FIELD

The present invention relates to methods of converting biomass to usefulsubstances, such as carboxylic acids and primary alcohols, through anintegrated pretreatment, fermentation, dewatering and treatment process.More specifically it may relate to a method applied to lignocellulosicbiomass.

BACKGROUND

A great deal of biomass, particularly lignocellulosic biomass, remainsunused or inefficiently used during agricultural and industrialprocesses. Disposal of this biomass is often difficult or costly.Therefore, methods of using this biomass to produce useful chemicals arequite valuable.

Organic acids are important chemicals of commerce. Historically, organicacids were produced from animal fat or vegetable oil sources or frompetroleum sources in substantially nonaqueous systems. More recently,organic acids have been identified as among the most attractive productsfor manufacture from biomass by fermentation. Alcohols are alsoimportant industrial chemicals that may be produced by fermentation ofbiomass. However, extraction of organic acids and alcohols from theoverall fermentation product is not easy and is often inefficient in theuse of energy, water and reactant chemicals.

SUMMARY OF THE INVENTION

The present invention includes a method, process and apparatus for theconversion of biomass to carboxylic acids and/or primary alcohols.

According to one embodiment, the invention includes a system for theconversion of biomass. The system includes a pretreatment/fermentationsubsystem operable to pretreat biomass with lime or quick lime and airto produce treated biomass and ferment the treated biomass with aninoculum to produce a fermentation broth containing carboxylic acidsalts. The system also includes a dewatering subsystem operable toremove excess water from the fermentation broth to produce aconcentrated product. Finally, the system includes an acid springingsubsystem operable to combine the concentrated product with alow-molecular-weight tertiary amine or ammonia to produce alow-molecular-weight tertiary amine or ammonia carboxylate product fromthe carboxylic acid salts, replace the low-molecular-weight tertiaryamine or ammonia in the low-molecular-weight tertiary amine or ammoniacarboxylate product with a high-molecular-weight tertiary amine to forma high-molecular-weight tertiary amine carboxylate product, andthermally break the amine-carboxylate bonds in the high-molecular-weighttertiary amine carboxylate product to produce a mixed carboxylic acidproduct.

In a more specific embodiment the system may also include ahydrogenation subsystem operable to combine the mixed carboxylic acidproduce with a high-molecular-weight alcohol to form an ester, convertthe ester to an alcohol mixture using a hydrogenation catalyst, andseparate the alcohol mixture from the high-molecular-weight alcohol.

According to another embodiment, the invention includes a method ofobtaining a fermentation product. The method may include: treating apile of biomass with lime or quick lime, water, an innoculum and air toproduce a fermentation broth; acidifying the fermentation broth with ahigh-molecular-weight carboxyllic acid to produce acidified fermentationbroth; stripping the fermentation broth in a stripping column to producestripped fermentation broth; concentrating the stripped fermentationbroth in an evaporator to produce concentrated product; mixing theconcentrated product with a low-molecular-weight tertiary amine orammonia and carbon dioxide to produce a low-molecular-weight tertiaryamine or ammonia carboxylate; exchanging the low-molecular-weighttertiary amine or ammonia carboxylate with a high-molecular-weighttertiary amine to produce a high-molecular-weight tertiary aminecarboxylate; heating the high-molecular-weight tertiary aminecarboxylate to a temperature sufficient to break acid/amine bonds toproduce a free carboxylic acid product; and recovering the freecarboxylic acid product.

In a more specific embodiment, the method may also include: combiningthe carboxylic acid produce with a high-molecular-weight alcohol to froman ester; hydrogenating the ester to form an alcohol product; separatingthe high-molecular-weight alcohol from the alcohol product; andrecovering the alcohol product.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be better understood through reference to thefollowing detailed description, taken in conjunction with the drawings,in which:

FIG. 1 illustrates a pretreatment and fermentation system, according toan embodiment of the present invention;

FIG. 2 illustrates a dewatering system, according to an embodiment ofthe present invention;

FIG. 3 illustrates an acid springing system, according to an embodimentof the present invention; and

FIG. 4 illustrates a hydrogenation system, according to an embodiment ofthe present invention.

DETAILED DESCRIPTION

The present invention relates to systems, methods, and devices for theconversion of biomass, particularly lignocellulosic biomass, tocarboxylic acids and alcohols, particularly primary alcohols.

Referring now to FIG. 1, pretreatment and filtration system 10 may beprovided in which biomass pile 12 may be blended with lime or quick lime(calcium carbonate or calcium oxide) and carbon dioxide (not shown) andpiled on top of pit 14 filled with gravel 16. Pit 14 may also be linedwith liner 18. Biomass pile 12 may include any sort of biomass. Inselected embodiments it may include lignocellulosic biomass, such asprocessed sugarcane or sorghum stalks or corn stover. Perforated drainpipe 20 may be embedded in gravel 16. Biomass pile 12 may be covered bycover 22 to keep out rain and debris, particularly if system 10 isoutside. Pump 24 may circulate water 34 from pit 14 to the top ofbiomass pile 12. As water 34 circulates through pile 12, it may flowthrough heat exchanger 26, which may regulate the temperature. Coolingwater or heat source 28 may also circulate through heat exchanger 26.

During approximately the first month after biomass pile 12 is assembled,air 38 may be blown through pile 12 using blower 30. To remove carbondioxide from the air, it may be bubbled through lime water slurry 32.Oxygen-rich air 28 may also be supplied. The combined effect of limeplus air 28 in pile 12 removes lignin from the biomass, rendering itmore digestible. Further, the lime removes acetyl groups fromhemicellulose, which also helps digestibility. Once the lime isexhausted, the pH drops to near neutral, at which point a mixed-cultureinoculum may be added.

The inoculum may be derived from any source, but in many embodiments itmay be derived from soil. Organisms derived from organic-rich soil inmarine environments appear to be particularly well-suited for use withembodiments of the present invention. Such organisms are able to beproductive in high-salt environments. For example, the innoculum mayinclude a salt-tolerant microorganism.

After inoculation, the organisms digest the biomass and convert it tocarboxylic acids. These acids react with the calcium carbonate orcalcium oxiode in pile 12, producing calcium carboxylate salts or othercalcium salts that are dissolved in the water that circulates throughthe pile. This aqueous solution, called fermentation broth 36 may beharvested and sent for further processing.

Referring now to FIG. 2, fermentation broth 36 may be dewatered indewatering system 40. Fermentation broth 26 may be pumped through heatexchanger 42, which preheats the broth. Preheated fermentation broth 36may then be acidified with high-molecular-weight carboxylic acid 46(e.g. caproic, valeric, hepotanoic acids). Acidified fermentation broth36 may be sent to stripping column 44 where steam 80 strips outdissolved carbon dioxide, a noncondensible gas that may interferes withevaporator 58 and cause calcium carbonate scaling on heat exchanger 56.Preferably, stripper 44 may operate at 1 atm, or higher, which allowsexiting steam 86 to be used for heat elsewhere in the process. Further,if heat exchanger 42 becomes fouled by dissolved calcium carbonate, thepressure in stripper 44 may be reduced, which lowers the temperature ofsteam exiting heat exchanger 42 and may reduce fouling. However, ifstripper 44 is operated at a reduced pressure, a vacuum pump (not shown)may be needed to remove the noncondensible gases from fermentation broth36.

Steam-stripped, acidified fermentation broth 36 may then be sent tomixer 48 where the pH may be raised to between approximately 11 and 12through the addition of lime 50 from reservoir 78, which causes scum 54to precipitate. Scum 54 may then be removed in solids separator 52. Thisdegassed, descummed fermentation broth 36 may be further heated in heatexchanger 56, after which it may enter evaporator 58. Compressor 60 mayevaporate water from the low-pressure chamber of evaporator 58. The heatof condensation released in the high-pressure chamber of evaporator 58may provide the heat of evaporation needed in the low-pressure chamber.The energy needed to drive the evaporation process may be provided by anengine.

In the embodiment shown in FIG. 2, a combined cycle engine may be used,which increases energy efficiency. Gas turbine 88 may provide shaftpower to compressor 60. Gas turbine may use fuel 74. Exhaust gas 72 fromgas turbine 88 may be directed to boiler 62, which may producehigh-pressure steam that may drives steam turbine 64. Heat exchanger 66may condense the low-pressure steam exiting steam turbine 64. Coolingwater 76 may be used to facilitate this cooling. Distilled water 82 fromthe high-pressure section of evaporator 58 may be cooled in heatexchangers 56 and 42, and may be returned to pretreatment/fermentationsystem 10. Concentrated product 68 may be cooled in heat exchangers 56and 42, and sent to acid springing system 90. Liquid turbine 70 mayrecapture some work from the high-pressure liquids that exit evaporator58.

Pumps 84 may be included at various points in the system to facilitatefluid flow.

Referring now to FIG. 3, concentrated product 68 may next be sent toacid springing system 90. In mixer 92, concentrated product 68 fromdewatering system 40 may be mixed with carbon dioxide 94 andlow-molecular-weight tertiary amine 96, such as triethyl amine. Thecarboxylate reacts with low-molecular-weight tertiary amine 96 to form asoluble salt. The calcium reacts with carbon dioxide 94 to forminsoluble calcium carbonate 98, which may be recovered using solidsseparator 100. Calcium carbonate 98 may then be washed with distilledwater to remove adhering product and steam stripped in vessel 102 toensure that all low-molecular-weight tertiary amine 96 is removed fromcalcium carbonate 98. Calcium carbonate 98 may then be sent topretreatment/fermentation system 10 to act as a buffer or to a lime kiln(not shown) to be converted to lime.

Aqueous solution 104 contains dissolved low-molecular-weight tertiaryamine carboxylate. It may then be preheated in heat exchanger 106 andsent to evaporator 108, where most of the water may be removed using thesame vapor-compression technology used in dewatering system 40.Specifically, turbine 130 may provide energy to compressor 132. Wastefluid exiting evaporator 108 may be sent to column 134 where it may becombined with lime 136 and steam 138 to provide additional productstream to mixer 92 and water 140 to pretreatment/fermentation system 10.

The concentrated low-molecular-weight tertiary amine carboxylatesolution 104 may then be sent to column 110 where high-molecular-weighttertiary amine 112, such as trioctyl amine or triethanol amine, may beadded. Low-molecular-weight tertiary amine 96 may be replaced and exitthe top of column 110, while high-molecular-weight tertiary aminecarboxylate solution 104 may exit the bottom of column 110.

The high-molecular-weight tertiary amine carboxylate solution 104 maythen be preheated in heat exchanger 114 and sent to column 116. Incolumn 116, the temperature may be high enough to break chemical bonds,allowing the more volatile carboxylic acids 146 to exit the top ofcolumn 116. The less volatile high-molecular-weight tertiary amine 112may exit the bottom of the column and may be recycled to column 110.

Any salts 120 that are in high-molecular-weight tertiary amine 112 maybe removed using a solids separator 118. Recovered salts 120 may bewashed with volatile solvent 122, such as triethyl amine, to removehigh-molecular-weight tertiary amine 112 in separator 118. Solvent 122may be separated from the recovered high-molecular-weight tertiary aminein distillation column 124. Salts 120 may then be steam stripped instripper 126 to remove volatile solvent 122 and form solids 144.

System 90 may contain various heat exchangers 140 that may be used torecycle process heat. Various fluids may pass through these heatexchangers, such as cooling waters 142, steam 148, and fuel 150. In oneheat exchanger 140, steam 86 from dewatering system 40 may be used as aheat source then collected in condenser 152 where carbon dioxide 154 maybe separated from water 156, which may be returned tofermentation/pretreatment system 10.

Pumps 158 may also be included at various points in the system tofacilitate fluid flow.

Referring now to FIG. 4, mixed carboxylic acids 146 from acid springingsystem 90 may be sent to hydrogenation system 170. Mixed acids 146 maybe placed in column 172 and combined with high-molecular-weight alcohol174 such as heptanol. Carboxylic acids 146 react with alcohol 174 toform ester 176 and water 178. Water 178 may be separated in column 172and sent to heat exchanger 180 then returned to column 172 or usedelsewhere in systems 10, 40, 90 or 170. Ester 176 may be sent tohydrogenation reactor 182 which contains a suitable hydrogenationcatalyst, such as a Raney nickel. In reactor 182, hydrogen 200 is addedand ester 176 is converted to alcohol. Solids may be separated fromalcohol 184 using solids separator 186. Alcohol mixture 184 may be sentcolumn 188 which may recover high-molecular-weight alcohol 174 from thebottom and alcohol product 190 from the top. Alcohol product 190 may bea primary alcohol.

System 170 may contain various heat exchangers 192 that may be used torecycle process heat. Various fluids may pass through these heatexchangers, such as cooling waters 194 and steam 196. Pumps 198 may alsobe included at various points in the system to facilitate fluid flow.

Alternative systems to recover carboxylic acids without production ofalcohol are known in the art any may be used in place of thehydrogenation system of FIG. 4.

Referring now to FIG. 5, system 300 may include as subsystems 302pretreatment/fermentation system 10, dewatering system 40, acid spriningsystem 90 and optionally also hydrogenation system 170. System 300 mayreuse process heat, water, lime, carbon dioxide and other materialsamong different subsystems 302.

In an alternative embodiment not explicitly shown, ammonia may be usedin place of low-molecular-weight tertiary amine 96 in acid spriningsystem 90. Further, if the ammonia is supplied earlier, the a reactionbetween calcium carboxylate, carbon dioxide and ammonia may occur priorto entry into dewatering system 40. In this embodiment, an aqueoussolution of ammonia carboxylate may be evaporated in dewatering system40 rather than calcium carboxylate. This may help prevent scaling inheat exchangers or system 40 because ammonium salts have a lessertendency to scale than calcium salts. Ammonia is also cheap and lostammonia may be diverted to pretreatment/fermentation system 10 where itmay serve as a nitrogen source. However, ammonia may react withcarboxylic acids to form amides, which may not be a desired byproduct.

Embodiments of the invention may include all processes involved in theoperation of the above-described systems. Referring now to FIG. 6, theinvention may include an integrated method for producing carboxylicacids and alcohols. The method may include treating pile of biomass 12with lime or quick lime, water 34, an innoculum and air in step 400 toproduce fermentation broth 36. In step 410, fermentation broth 36 may beacidified with high-molecular-weight carboxylic acid 46 then, in step420, stripped in stripping column 44. In step 430, the product may beconcentrated in evaporator 58 to produce concentrated product 68.Concentrated product 68 may be mixed with carbon dioxide 94 andlow-molecular-weight tertiary amine 96 in step 440 to form alow-molecular-weight tertiary amine carboxylate. This carboxylate may beexchanged with high-molecular-weight tertiary amine 112 in column 110 instep 450 to produce a high-molecular-weight tertiary amine carboxylate.The high-molecular-weight tertiary amine carboxlate may be heated incolumn 116 to a temperature high enough to break the acid to amine bondsin step 460. This produces carboxylic acids 146 which may be recoveredin step 470. In some embodiments, carboxylic acids 146 may be combinedwith high-molecular-weight alcohol 174 to form ester 176 in step 480. Instep 490, ester 176 may be hydrogenated in chamber 182 to form alcoholproduct 190. In step 500, high-molecular-weight alcohol 174 and alcoholproduct 190 may be separated in column 188. Alcohol product 190 may be aprimary alcohol.

In an alternative embodiment, ammonia may be used in place oflow-molecular-weight tertiary amine 96. Ammonia may be added immediatelyafter step 400.

Various methods, systems and apparati useful in the present inventionmay also be described in U.S. Pat. No. 6,043,392, issued Mar. 28, 2000,U.S. Pat. No. 5,986,133, issued Nov. 16, 1999, U.S. Pat. No. 6,478,965,issued Nov. 12, 2002, U.S. Pat. No. 6,395,926, issued May 28, 2002, U.S.Pat. No. 5,962,307, issued Oct. 5, 1999, and WO 04/041995, published May21, 2004, and their US and foreign counterpart applications and patents.All of the above patents and applications are incorporated by referenceherein.

1. A system for the conversion of biomass comprising: apretreatment/fermentation subsystem operable to: pretreat biomass withlime or quick lime and air to produce treated biomass; and ferment thetreated biomass with an inoculum to produce a fermentation brothcontaining carboxylic acid salts; a dewatering subsystem operable to:remove excess water from the fermentation broth to produce aconcentrated product; and an acid springing subsystem operable to:combine the concentrated product with a low-molecular-weight tertiaryamine or ammonia to produce a low-molecular-weight tertiary amine orammonia carboxylate product from the carboxylic acid salts; replace thelow-molecular-weight tertiary amine or ammonia in thelow-molecular-weight tertiary amine or ammonia carboxylate product witha high-molecular-weight tertiary amine to form a high-molecular-weighttertiary amine carboxylate product; and thermally break theamine-carboxylate bonds in the high-molecular-weight tertiary aminecarboxylate product to produce a mixed carboxylic acid product.
 2. Asystem according to claim 1, further comprising a hydrogenationsubsystem operable to: combine the mixed carboxylic acid produce with ahigh-molecular-weight alcohol to form an ester; convert the ester to analcohol mixture using a hydrogenation catalyst; and separate the alcoholmixture from the high-molecular-weight alcohol.
 3. A system according toclaim 1, where the biomass comprises lignocellulosic biomass.
 4. Asystem according to claim 1, wherein the pretreatment/fermentationsubsystem further comprises: a pit having: a liner; gravel placed on theliner; and a perforated drain pipe embedded in the gravel; a biomasspile located on top of the pit; a cover over the biomass pile; and apump operable to circulate water from the pit to the top of the biomasspile.
 5. A system according to claim 4, wherein thepretreatment/fermentation subsystem further comprises: a blower operableto circulate air through the biomass pile; and a lime water slurryoperable to remove carbon dioxide from the air.
 6. A system according toclaim 1, wherein the innoculum comprises a salt-tolerant microorganism.7. A system according to claim 1, wherein the dewatering subsystemfurther comprises: a high-molecular-weight carboxylic acid added to thefermentation broth to produce acidified fermentation broth; and anevaporator operable to concentrate the acidified fermentation broth. 8.A system according to claim 7, wherein the high-molecular-weightcarboxylic acid comprises caproic acid, valeic acid or hepotanoic acid.9. A system according to claim 1, wherein the acid springing subsystemfurther comprises: a mixer to operable to mix the concentrated productwith the low-molecular-weight tertiary amine or ammonia and carbondioxide; a column operable to exchange the low-molecular-weight tertiaryamine or ammonia in the low-molecular-weight tertiary amine or ammoniacarboxylate product for a high-molecular-weight tertiary amine; and acolumn operable to thermally break the amine-carboxylate bonds in thehigh-molecular-weight tertiary amine carboxylate product to produce amixed carboxylic acid product.
 10. A system according to claim 1,wherein the low-molecular-weight tertiary amine comprises triethylamine.
 11. A system according to claim 1, wherein thehigh-molecular-weight tertiary amine comprises trioctyl amine ortriethanol amine.
 12. A system according to claim 2, wherein thehydrogenation subsystem further comprises: a column operable to combinethe mixed carboxylic acid produce with a high-molecular-weight alcoholto form an ester; a hydrogenation reactor operable to convert the esterto an alcohol mixture using a hydrogenation catalyst; and a columnoperable to separate the alcohol mixture from the high-molecular-weightalcohol.
 13. A system according to claim 2, wherein thehigh-molecular-weight alcohol comprises heptanol.
 14. A system accordingto claim 2, wherein the alcohol mixture substantially comprises primaryalcohols.
 15. A system according to claim 1, further comprising thesystem operable to recycle process heat within at least one subsystem orfrom one subsystem to another.
 16. A system according to claim 1,further comprising the system operable to recycle water within at leastone subsystem or from one subsystem to another.
 17. A system accordingto claim 1, further comprising the system operable to recycle lime orquick lime within at least one subsystem or from one subsystem toanother.
 18. A system for the conversion of biomass comprising: apretreatment/fermentation means operable to: pretreat biomass with limeor quick lime and air to produce treated biomass; and ferment thetreated biomass with an inoculum to produce a fermentation brothcontaining carboxylic acid salts; a dewatering means operable to: removeexcess water from the fermentation broth to produce a concentratedproduct; and an acid springing means operable to: combine theconcentrated product with a low-molecular-weight tertiary amine orammonia to produce a low-molecular-weight tertiary amine or ammoniacarboxylate product from the carboxylic acid salts; replace thelow-molecular-weight tertiary amine or ammonia in thelow-molecular-weight tertiary amine or ammonia carboxylate product witha high-molecular-weight tertiary amine to form a high-molecular-weighttertiary amine carboxylate product; and thermally break theamine-carboxylate bonds in the high-molecular-weight tertiary aminecarboxylate product to produce a mixed carboxylic acid product.
 19. Asystem according to claim 18, further comprising a hydrogenation meansoperable to: combine the mixed carboxylic acid produce with ahigh-molecular-weight alcohol to form an ester; convert the ester to analcohol mixture using a hydrogenation catalyst; and separate the alcoholmixture from the high-molecular-weight alcohol.
 20. A method ofobtaining a fermentation product comprising: treating a pile of biomasswith lime or quick lime, water, an innoculum and air to produce afermentation broth; acidifying the fermentation broth with ahigh-molecular-weight carboxyllic acid to produce acidified fermentationbroth; stripping the fermentation broth in a stripping column to producestripped fermentation broth; concentrating the stripped fermentationbroth in an evaporator to produce concentrated product; mixing theconcentrated product with a low-molecular-weight tertiary amine orammonia and carbon dioxide to produce a low-molecular-weight tertiaryamine or ammonia carboxylate; exchanging the low-molecular-weighttertiary amine or ammonia carboxylate with a high-molecular-weighttertiary amine to produce a high-molecular-weight tertiary aminecarboxylate; heating the high-molecular-weight tertiary aminecarboxylate to a temperature sufficient to break acid/amine bonds toproduce a free carboxylic acid product; and recovering the freecarboxylic acid product.
 21. A method according to claim 20 furthercomprising: combining the carboxylic acid produce with ahigh-molecular-weight alcohol to from an ester; hydrogenating the esterto form an alcohol product; separating the high-molecular-weight alcoholfrom the alcohol product; and recovering the alcohol product.
 22. Amethod according to claim 20, wherein the biomass compriseslignocellulosic biomass.
 23. A method according to claim 22, wherein thealcohol produce substantially comprises primary alcohols.